(1) Field of the Invention
The present disclosure relates to a compound cycle rotary engine that offers low specific fuel consumption at high power to weight. The compound cycle rotary engine has particular utility for propulsion systems.
(2) Prior Art
Gas turbine engines in the 500 to 3000 shaft horsepower range are well known for having very high power to weight (power produced per unit weight), but at high specific fuel consumption (fuel flow rate per unit power, SFC). Intermittent combustion engines (e.g. spark ignition, or SI, reciprocating engines and compression ignition, or CI, reciprocating engines) are well known for having low SFC, but at low power to weight. It is desirable to achieve low SFC at high power to weight. A compound engine cycle which combines certain features of both engine types has the potential to achieve low specific fuel consumption at relatively high power to weight.
Compound engine cycles are well documented in the literature and textbooks. In a typical compound cycle engine, energy is extracted from the exhaust stream of a reciprocating engine by expanding the exhaust gas through a turbine. The turbine drives a shaft that is linked through a gearbox or fluid coupling to the main engine output shaft, thus increasing the total system power output. The reciprocating engine is typically otherwise conventional in nature and may be either a CI or SI engine. In addition to the compound cycle turbine, conventional turbochargers may be fitted in essentially the same manner as they are to non-compound cycle engines. Turbochargers are used to increase the power and/or efficiency of an engine. Intercoolers may also be fitted to increase charge density and/or control combustion temperatures. Variations on this configuration are also well documented.
Previous attempts have been made to develop a compound cycle engine (CCE) utilizing a compression ignition (CI) reciprocating engine core. While these engines have been successful in achieving low SFCs (around 0.33 lbm/hr/hp), they have not achieved high power to weight (exceeding 2.0 hp/lbm). This is due primarily to the reciprocating masses (pistons), valves and combustion systems inherent in a CI engine that limits the engine's ability to operate at high speed. The higher the engine operating speed, the more power that can be produced for a given volume and thus the higher the power to weight. Also, the chamber pressures and temperatures at which CI engines operate require heavy structures for containment.
Thus, there remains a need for a compound cycle engine which is capable of achieving low specific fuel consumption at relatively high power to weight.